popup instead of black bar

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I need a popup for lo-gin register instead of the black bar on top. Howto do that?

I have set it to not to show the price when people/clients are not logged in. I want to show the popup instead when one clicks on a product and isn't registered or logged in.

Thank you in advance for your kind advice

This message is displayed via Joomla! build in message system and you can achieve pop-up message without some many changes in javascript and message block code.